How To Increase Size Of Outlook Mailbox – Space Management And Cleanup Tools

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Increasing the size of your Outlook mailbox can be achieved by cleaning out the Deleted Items and Sent Items folders. If you are searching for how to increase size of outlook mailbox, you are likely seeing a dreaded “mailbox full” warning. This guide gives you practical steps to free up space and avoid those storage limits.

Outlook mailboxes have storage caps set by your email provider, like Microsoft 365 or Exchange. When you hit that limit, you cannot send or receive new emails. The good news is you have several ways to reclaim space without losing important messages.

How To Increase Size Of Outlook Mailbox

Before you start, check your current mailbox size. In Outlook, go to File > Account Settings > Account Settings. Select your email account and click “Change.” Look for “Mailbox Size” or “More Settings.” This shows you how much space you are using.

Clear Out Deleted Items Folder

Your Deleted Items folder holds every email you removed. These still count against your mailbox size. Empty this folder regularly to recover space fast.

  1. Open the Deleted Items folder in Outlook.
  2. Select all messages by pressing Ctrl + A.
  3. Right-click and choose “Delete All.”
  4. Alternatively, go to Folder > Clean Up > Empty Deleted Items Folder.

You can also set Outlook to auto-empty this folder every time you close the program. Go to File > Options > Advanced. Under “Outlook start and exit,” check “Empty Deleted Items folders when exiting Outlook.”

Manage Sent Items Folder

Your Sent Items folder stores copies of every email you send. Over time, this can become huge. Delete old sent emails you no longer need.

  • Sort Sent Items by date to find old messages.
  • Select and delete emails older than six months.
  • Consider moving important sent emails to a local archive folder.

You can also turn off saving sent items for specific emails. When composing a message, go to Options > Save Sent Item. Uncheck “Save sent item.” This is useful for one-time replies or internal notes.

Use AutoArchive To Move Old Emails

AutoArchive automatically moves old emails to a local data file (.pst). This reduces your mailbox size while keeping messages accessible.

  1. Go to File > Options > Advanced.
  2. Click “AutoArchive Settings.”
  3. Check “Run AutoArchive every 14 days” (or your preferred interval).
  4. Set “Archive items older than” to 3, 6, or 12 months.
  5. Choose “Move old items to” and select a location for the .pst file.
  6. Click OK.

After setup, Outlook runs AutoArchive automatically. You can access archived emails by opening the .pst file in Outlook.

Empty Junk Email Folder

Your Junk Email folder holds spam and unwanted messages. These also take up space. Empty this folder regularly.

  • Open the Junk Email folder.
  • Select all messages (Ctrl + A).
  • Right-click and choose “Delete.”
  • Or go to Home > Delete > Empty Folder.

Set your junk filter to automatically delete items after 30 days. Go to Home > Junk > Junk E-mail Options. Under “Options,” choose “Permanently delete suspected junk email instead of moving it to the Junk E-mail folder.”

Delete Large Attachments

Emails with large attachments eat up mailbox space quickly. Find and remove these attachments to free up significant storage.

  1. In Outlook, go to your Inbox.
  2. Click the search bar and type “size:>5 MB” (or “size:>10 MB” for bigger files).
  3. This shows all emails with attachments over 5 MB.
  4. Delete emails you no longer need, or save attachments to your computer and remove them from the email.

To remove attachments without deleting the email: Open the email, right-click the attachment, and choose “Remove Attachment.” The email body stays, but the file is gone.

Use Online Archive (For Microsoft 365 Users)

If you have a Microsoft 365 Business or Enterprise plan, you may have an Online Archive. This is a separate mailbox that stores old emails automatically.

  • Check if Online Archive is enabled: Go to File > Account Settings > Account Settings. Select your account and click “Change.” Look for “Online Archive” under mailbox settings.
  • If enabled, Outlook shows a separate “Online Archive” folder in the folder pane.
  • Move old emails manually or set up a retention policy to auto-archive.

Your IT administrator can enable Online Archive if it is not active. This feature does not count against your primary mailbox limit.

Compact Your Outlook Data File

Even after deleting emails, your .pst or .ost file may still be large. Compacting it reclaims unused space.

  1. Close Outlook.
  2. Open Control Panel > Mail (32-bit).
  3. Click “Data Files.”
  4. Select your data file and click “Settings.”
  5. Click “Compact Now.”
  6. Wait for the process to finish (it may take several minutes).

This step is safe and does not delete any data. It simply reorganizes the file to remove gaps left by deleted items.

Use Mailbox Cleanup Tools

Outlook has built-in tools to help you find and delete large or old items.

  • Go to File > Tools > Mailbox Cleanup.
  • Click “Find items larger than” to see emails over a certain size.
  • Click “Find items older than” to see emails from a specific date.
  • Use “AutoArchive” or “Empty Deleted Items” from this same window.

These tools give you a quick overview of what is taking up space. You can then delete or archive items in bulk.

Move Emails To Local Folders

If your mailbox is on an Exchange server, you can move emails to local .pst folders on your computer. This removes them from the server but keeps them accessible in Outlook.

  1. Create a new local .pst file: Go to File > Account Settings > Account Settings > Data Files > Add.
  2. Name the file (e.g., “Archive 2024”) and choose a location.
  3. Drag and drop emails from your mailbox folders to the new .pst folder.

Be aware that .pst files are not backed up to the cloud. If your computer crashes, you may lose these emails. Always back up your .pst file to an external drive or cloud storage.

Reduce Email Retention Period

Your email provider may have a default retention policy that keeps deleted items for 30 days or more. Shortening this period frees up space faster.

  • In Outlook, go to File > Account Settings > Account Settings.
  • Select your account and click “Change.”
  • Look for “More Settings” > “Advanced.”
  • Under “Mailbox Settings,” find “Retention Policy.”
  • Set “Deleted items retention period” to 14 days or less.

This change applies to your entire mailbox. Items in Deleted Items older than the set period are permanently removed.

Use Third-Party Tools

If manual cleanup is too time-consuming, consider third-party tools. These scan your mailbox and help you delete large emails, duplicate items, and old messages.

  • Tools like MailStore Home, SysTools Outlook Cleaner, or Stellar Mailbox Cleaner are popular.
  • Most offer free trials so you can test before buying.
  • Always download from official websites to avoid malware.

These tools can automate the process, but be careful. Always back up your mailbox before using any third-party software.

Request A Mailbox Size Increase

If you have tried everything and still need more space, ask your IT administrator or email provider to increase your mailbox limit.

  • For Microsoft 365: Plans range from 50 GB to 100 GB. Some plans allow unlimited archiving.
  • For Exchange: Administrators can set custom limits.
  • For personal accounts (like Outlook.com): Limits are usually 15 GB. You can upgrade to Microsoft 365 for more space.

This is the simplest solution if your organization allows it. But it may not be available for all account types.

Enable Cached Exchange Mode

Cached Exchange Mode downloads a copy of your mailbox to your computer. This reduces server load and can help with performance, but it does not increase mailbox size. However, it lets you work offline and sync changes later.

  1. Go to File > Account Settings > Account Settings.
  2. Select your account and click “Change.”
  3. Check “Use Cached Exchange Mode.”
  4. Set “Download email for the past” to 1 month or 3 months.

This setting reduces the amount of data stored locally, but your server mailbox remains unchanged. It is useful if you have a slow connection or limited local storage.

Use Focused Inbox

Focused Inbox separates important emails from less important ones. While it does not directly increase mailbox size, it helps you spot and delete unwanted messages faster.

  • Go to View > Show Focused Inbox.
  • Review the “Other” tab for emails you can delete.
  • Move unwanted senders to Junk or block them.

This is a small habit that keeps your mailbox lean over time.

Regular Maintenance Schedule

To avoid hitting your mailbox limit again, set up a regular cleanup routine.

  • Weekly: Empty Deleted Items and Junk Email folders.
  • Monthly: Delete old Sent Items and large attachments.
  • Quarterly: Run AutoArchive or move emails to local folders.
  • Yearly: Compact your data file and review your retention settings.

Stick to this schedule, and you will rarely see the “mailbox full” warning.

Frequently Asked Questions

What Is The Maximum Size Of An Outlook Mailbox?

It depends on your email plan. Microsoft 365 Business Basic gives 50 GB. Microsoft 365 Business Standard gives 100 GB. Personal Outlook.com accounts have 15 GB. Exchange on-premises limits are set by your IT administrator.

Does Deleting Emails From Outlook Free Up Server Space?

Yes, if you empty the Deleted Items folder. Simply deleting emails moves them to Deleted Items, where they still count against your limit. Empty that folder to reclaim space on the server.

Can I Increase Outlook Mailbox Size Without Deleting Emails?

Yes. You can use AutoArchive to move old emails to a local .pst file, or use Online Archive if your plan supports it. This keeps emails accessible without using your primary mailbox storage.

Why Is My Outlook Mailbox Still Full After Deleting Emails?

You may need to empty the Deleted Items folder and compact your data file. Also check if your Sent Items, Junk Email, or other folders hold large items. Use the Mailbox Cleanup tool to find hidden space hogs.

How Often Should I Clean My Outlook Mailbox?

Weekly for Deleted Items and Junk Email. Monthly for Sent Items and large attachments. Quarterly for archiving old emails. This routine prevents your mailbox from filling up again.

By following these steps, you can effectively manage your Outlook mailbox size. Start with the quick wins like emptying Deleted Items and Sent Items. Then move to AutoArchive and attachment cleanup. With regular maintenance, you will never have to worry about a full mailbox again.